Monday, November 12, 2012

In 52 B.C. Julius Caesar, near the end of his war against Gaul, had one great enemy left – the charismatic
Arvernian, Vercingetorix. Expelled from Gergovia, for being too rash,
Vercingetorix raised an army on his own, and assumed the role of commander. His
strategy against Caesar was simple -- use superior cavalry to harass the Romans
and drive them away. Caesar, understanding his own weakness, compensated by
recruiting Germans to strengthen his own cavalry units. After a series of
reversals, Vercingetorix was forced to retreat to the walled city of Alesia with his army of
80,000.

No obstacle would deter Caesar, however. He knew direct
attack was impossible because of the hilltop position of the city, so he
planned a siege to starve the Gauls into surrender. Caesar had 12 legions with auxiliaries
ready to bring to bear on the enemy. It was mid-summer, 52 B.C.

The image above shows the Gallic camp, town of Alesia, and
the Roman fortifications.

This image is a view from the west showing the geography.

For this post we focus on the engineering aspects of the
battle, as we did with the Masada and Rhine
bridge posts. Here again the tenacity of the Roman people and the skill of their engineers would provide the margin of victory.

Let’s start with The Conquest of Gaul Book 7 chapter LXIX to
set the scene.

“The town itself was situated on the top of a hill, in a
very lofty position, so that it did not appear likely to be taken, except by a
regular siege. Two rivers, on two different sides, washed the foot of the hill.
Before the town lay a plain of about three miles in length; on every other side
hills at a moderate distance, and of an equal degree of height, surrounded the
town. The army of the Gauls had filled all the space under the wall, comprising
the part of the hill which looked to the rising sun, and had drawn in front a
trench and a stone wall six feet high. The
circuit of that fortification, which was commenced by the Romans, comprised
eleven miles. The camp was pitched in a strong position, and twenty-three redoubts
were raised in it, in which sentinels were placed by day, lest any sally should
be made suddenly; and by night the same were occupied by watches and strong
guards.”

Before the circumvallation could be completed, however, Vercingetorix
sent a party of tribal leaders through the breech on a mission to recruit
allies and bring them back as reinforcements. We move on to chapter LXXII.

“Caesar, on learning these proceedings from the deserters
and captives, adopted the following system of fortification; he dug a trench
twenty feet deep, with perpendicular sides, in such a manner that the base of
this trench should extend so far as the edges were apart at the top. He raised
all his other works at a distance of four hundred feet from that ditch; [he
did] that with this intention, lest (since he necessarily embraced so extensive
an area, and the whole works could not be easily surrounded by a line of
soldiers) a large number of the enemy should suddenly, or by night, sally
against the fortifications; or lest they should by day cast weapons against our
men while occupied with the works. Having left this interval, he drew two
trenches fifteen feet broad, and of the same depth; the innermost of them,
being in low and level ground, he filled with water conveyed from the river.
Behind these he raised a rampart and wall twelve feet high: to this he added a
parapet and battlements, with large stakes cut like stags' horns, projecting
from the junction of the parapet and battlements, to prevent the enemy from
scaling it, and surrounded the entire work with turrets, which were eighty feet
distant from one another.”

Then the Romans began to construct the countervallation.

This photo shows the hills of Alesia from the Roman line.

Above is a portion of the reconstructed Roman fortifications.

“It was necessary, at one and the same time, to procure
timber [for the rampart], lay in supplies of corn, and raise also extensive
fortifications, and the available troops were in consequence of this reduced in
number, since they used to advance to some distance from the camp, and
sometimes the Gauls endeavored to attack our works, and to make a sally from
the town by several gates and in great force. On which Caesar thought that
further additions should be made to these works, in order that the
fortifications might be defensible by a small number of soldiers. Having,
therefore, cut down the trunks of trees or very thick branches, and having
stripped their tops of the bark, and sharpened them into a point, he drew a
continued trench everywhere five feet deep. These stakes being sunk into this
trench, and fastened firmly at the bottom, to prevent the possibility of their
being torn up, had their branches only projecting from the ground. There were
five rows in connection with, and intersecting each other; and whoever entered
within them were likely to impale themselves on very sharp stakes. The soldiers
called these "cippi." Before these, which were arranged in oblique
rows in the form of a quincunx, pits three feet deep were dug, which gradually
diminished in depth to the bottom. In these pits tapering stakes, of the
thickness of a man's thigh, sharpened at the top and hardened in the fire, were
sunk in such a manner as to project from the ground not more than four inches;
at the same time for the purpose of giving them strength and stability, they
were each filled with trampled clay to the height of one foot from the bottom:
the rest of the pit was covered over with osiers and twigs, to conceal the
deceit. Eight rows of this kind were dug, and were three feet distant from each
other. They called this a lily from its resemblance to that flower. Stakes a
foot long, with iron hooks attached to them, were entirely sunk in the ground
before these, and were planted in every place at small intervals; these they
called spurs.

…After completing
these works, having selected as level ground as he could, considering the
nature of the country, and having enclosed an area of fourteen miles, he
constructed, against an external enemy, fortifications of the same kind in
every respect, and separate from these, so that the guards of the
fortifications could not be surrounded even by immense numbers, if such a
circumstance should take place owing to the departure of the enemy's cavalry;
and in order that the Roman soldiers might not be compelled to go out of the
camp with great risk, he orders all to provide forage and corn for thirty days.”

In late September, a relief force of eighty thousand Gauls arrived
and both Gallic forces attacked the Romans – one from the inside and one from
the outside. Caesar sent his cavalry against the relief force while his army
fought off an attack from those trying to breakout from the city. Neither
Gallic army was able to penetrate the fortifications. The next day Vercingetorix
concentrated a new attack force against a weak spot in the inner
fortifications. His army successfully broke through but were attacked from
behind by Roman cavalry that had ridden around the outer ring to their rear.
Caesar, himself, appeared with the troops trying to close the gap and the
Romans were ultimately successful.

With their reinforcements routed, and no further hope to
break the siege, Silesia
surrendered and handed over Vercingetorix to Caesar, who imprisoned him for six
years and then paraded him through Rome
before his execution.

1 comment:

Did they exactly find in Alise what Caesar described ? Is it a problem if not ? How 80 000 gallic warriors could have been stupid enougth to let 60 000 roman have them locked on the top of such a little hill with less than 12m² per men + cattle + slaves + civilians etc...and less than 5m² if you consider "The army of the Gauls had filled all the space under the wall, comprising the part of the hill which looked to the rising sun" that means they settled out of the town? Two month croweded there with less than 1l of water a day...only for the warriors, none for their crew nor for the cattle(Vidal-Petit 2010)? Why 200 000 Gallic that gathered there to deliver Vercingetorix only attaqued in 2 points, once with just cavalry, another whith 60000 infantery when they could outmatch roman army by attacking on every side, 4 against one, more if you add the besieged 80.000? The Gauls still at war against each other or against the Germans and then 8 years against Romans, eager to imitate the inventions and military strategies of their opponents, according to Caesar, able to mobilize tens of millers warriors for months , were they finally that mindless barbarians incapable of conceiving a strategy other than running into the pile?